JPS5857760A - Photo semiconductor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor photodetector, and particularly to a light receiving element suitable for realizing high sensitivity, low dark current, and high speed performance.

Conventionally, a light receiving element having a mesa type or planar type structure as shown in FIGS. 1(a) and 1(b) has been proposed.

A first conductivity type semiconductor layer 02 and a second conductivity type semiconductor layer 03 are formed on a semiconductor substrate O1, and further an electrode 08 is formed.
．． 09 is provided. In a mesa-type structure as shown in FIG. 1(a), a high electric field is exposed at the bonding end face, so the device characteristics are influenced by the properties of the surface protection film, which is not desirable in practice. On the other hand, the planar structure shown in Fig. 1 fb) (Publication of Patent Publication No. 1987-1:32079)
It is expected that this structure will provide more stable operation than a mesa structure. In the structure of FIG. 1(b), the InP semiconductor substrate 1
There is an n+ type InP layer 2 + InGaAsP layer 3 on top. and an n-type InP layer. 6 is a Cd diffusion layer, for example, and a pn junction is formed at the end face of this diffusion layer. 7 is an insulating layer, and 8.9 is an electrode. However, there are drawbacks as described below.

When an InP crystal is used as a material with a large forbidden band width, it is conceivable that P, which has a high vapor pressure, dissociates in the heat treatment step of the device fabrication process after crystal growth, and the surface layer is altered. Therefore, the interfacial properties after the surface protective film is formed become unstable, causing an increase in dark current.

In general, in semiconductor materials, the smaller the effective mass and bandgap width, and the lower the impurity concentration, the lower the electric field strength that causes breakdown due to the tunnel effect. When the distance I between the formed pn junction surface and a region with a small forbidden band zero width (e.g., InGaAaP) is small, before the pn junction formed in the region with a large forbidden band width causes an avalanche multiplication effect, The electric field of a material with a small forbidden band width reaches an electric field sufficient to cause a tunnel effect, resulting in tunnel breakdown.

Generally, tunnel current can be expressed by the following formula:
Effective mass, q: Electron charge element, 1i=h/2π: h is blank constant, N: Impurity concentration E2=: Forbidden flow, f: Dielectric pole, b-e electric field strength Assuming that the junction is step-shaped Then, the relationship between the electric field strength and the operating voltage (tunnel breakdown voltage vT) is expressed by the following formula.On the other hand, the γ(Lanche breakdown voltage vA) is given by the following formula.

Now, taking a pn junction made of InGaAsP as an example, V
When determining the impurity concentration where T=vA, it is as follows.

I n P fE, candle λ: 1.35 μm):
~3X1017an-”In0.79()aO,21
"0.47 PO, 53 (", corresponding λ-1, 211m)
:~2X10 crn In0.7fiGa0.25”0.56P0.44 (
E, corresponding λ = t, 3 μm) ~ 7
Correspondence λ:! 1.55μm) 8 X l 014offl
” In order for avalanche multiplication to occur effectively, v, r＞
Since it is necessary that v□, the impurity concentration needs to be lower than the above value. Therefore, Fig. 1(b)
If the structure shown in is made, depending on the impurity concentration of the material with a large bandgap width and j, the restriction on the impurity concentration of the material with a small bandgap width will be relaxed somewhat, but in order to expect avalanche multiplication effect, , in a material with a large forbidden band width, the relationship vT > vA holds, and the maximum electric field E in a region with a small forbidden band width is the electric field strength E, r at tunnel breakdown (depending on the impurity concentration, the avalanche It is important to design the element so that the electric field strength at breakdown is smaller than the electric field strength vEA). If the distance 1 and the impurity concentrations of substances with large and small bandgap widths are NL and N, respectively, then in order to satisfy the above conditions, at least the following relationship must be satisfied between them. .

Therefore, there is a mutual relationship between NL, 4, and E7, and NL and N
The smaller 8 is, the larger 1 needs to be.

For example, NL=1 xl 016 Cm-31N, =2
In the case of 810"cm""l, I is about 1.5 μm or more for InGaAsP where λ==1.55 μm.

In this example, considering the above relationship, 1 is 1 μm.
In the following element design, the wavelength corresponding to the forbidden band width is 1.3 μm or 1.5 μm.
In a device configuration using Asp as a material with a small forbidden band width, the tunnel effect has a significant effect, making it difficult to create an effective avalanche photodiode.

On the other hand, when producing a photodiode having the structure shown in FIG. 1(b), although the maximum electric field during operation becomes small, it is necessary to limit the impurity concentration in the region where the forbidden band width is small. When the depletion layer widens by W in the region where the forbidden band width is small, the electric field strength E8 of the material with the small forbidden band 1 on the material side where the forbidden band width is large is given by the following equation.

If the depletion layer is (t+W) and W is 1 μm, then E,
Is it E? In order to prevent the impurity concentration N from exceeding the following value, it is necessary to make the impurity concentration N smaller than the following value.

N: approximately I x 10 membrane 6cm-”foeλ=1
．． 55μm approximately 2×10 cm fOrλ=1.3μ
As mentioned above, it is necessary to consider the relationship between E7 and N8 of the substance. In compound semiconductors, the lifetime of photoexcited carriers is extremely short compared to Si, so in order to increase the photoelectric conversion efficiency, the light absorption region must be made into a depletion layer, and in order to increase the speed, the junction capacitance must be reduced. In order to reduce C, it is necessary to expand the depletion layer. Junction capacitance is approximately given by the following equation.

C knee S (61j+W a: dielectric constant S: junction area Considering the practically required quantum efficiency (250%) and junction capacitance (2PF), it is considered necessary for the depletion layer W to expand by about 1 μm.

The object of the invention is to eliminate the aforementioned drawbacks,
The object of the present invention is to provide a high-speed light-receiving element with high sensitivity and low dark current.

A typical example of the present invention is shown in FIG. The first feature is that a material layer 14 with a large forbidden band width, which becomes an optical window layer, is formed on a material layer 13 with a small territorial band width, which becomes an active region.
By forming a polyatomic material layer 15 containing atoms of the material composition and protecting it with a surface protective film 17, the dark current is reduced and the interface is stabilized. It is characterized by a light-receiving element structure designed to

In addition, the second feature is the area 1 as explained above.
4 and the impurity concentration N14 of the material of region 13 and N8.
There is a relationship of N, 4≧N, 3, and Nts is 2
The light receiving element structure is characterized in that it has a width of 10"cm""3 or less.

One embodiment according to the present invention is shown in FIG. 2, and its structure will be described below.

Approximately 10"cm-" or more o High impurity concentration n+ type In
P substrate, 11. The impurity concentration is 9 x 10"Cm-" and the thickness is 1.5cm by a known liquid phase epitaxial growth method.
5 μm n-type InP layer, 12. is formed, and then the impurity concentration is 7×10Il1cm−”, F'J,
．． 3μm n-type “lLSI Gaall ASO,!I
s P,, 17 layers, 13. form. Especially 1.3μm
This In1-
A composition of 7≧X≧0.25 is preferable. Note that the A8 content is generally determined in accordance with the Ga content.

The relational expression y=0.48043+0.00327X exists. Subsequently, the impurity concentration is 9×1
0"cm"", 1.8μm thick n-type InPli!
14, and finally, an impurity concentration of 7×10”c
m, 0.2 μm thick n-type In,, Gacl,,
Continuously form As, 2P (La layer, 15.A
After forming the 12O3 and 5in2 films by a known vapor phase chemical reaction method, unnecessary portions of the Al2O3 and S+02 films were removed by a known selective photoetching method, and then the region 15 was removed and the above insulator was diffused. Zn or Cd impurities are introduced into the regions 14 and 15 using a diffusion method known as a mask, and P with a diffusion depth of 0.7 μm is introduced.
+-shaped diffusion region, 16. form. Diffusion layer, 16. and InP layer, 14. A pn junction is formed. pn
Joint surface and area, ]3. The distance between the two is 11 μm. Next, after removing the insulating layer used as a diffusion mask, a 5in2 film is formed by a known method of removal. After removing the unnecessary portions of Sin by a known selective photoetching method, a surface preservation film 17 is obtained. still.

As the anti-reflection film 17', a surface protective film was applied, or SiOt, Si, or N4 was re-formed and applied to a thickness suitable for an anti-reflection film. After this surface electrode,
18. and a back electrode 19 were formed. This device was observed to operate as an n1 device when mounted on a suitable stem.

The configuration and operation of this embodiment will be explained below. In this embodiment, since the region #R13 with a narrow forbidden band width is surrounded by the region with a wide forbidden band width, the incident light is absorbed in the region 13, resulting in a layered structure. In addition, the surface layer has a wide forbidden band I
It is formed of an nGaAsP layer, and an insulating film for surface protection is formed on top of it, making the characteristics at the interface stable.
Suitable for reducing dark current. This surface layer semiconductor layer can (1) be lattice matched with the underlying second semiconductor layer;
(2) Can they have the same crystal system? (3) Can they be exposed to high temperatures? It has properties such as being more stable than the No. 42 semiconductor layer.

This surface layer also has a higher band band than the semiconductor material of the active region.
Select a large composition of gears and pumps. The pn junction is formed at a distance from region 13 based on the above-mentioned idea, and the impurity concentration distribution is also taken into consideration, so that it maintains hard junction characteristics and efficiently transfers photoexcited carriers to the junction. suitable for collecting. In addition, since the spread of the depletion layer is set in consideration of the electric field distribution, the junction capacitance is reduced and it is suitable for high speed.◎ When this device is biased in the reverse direction, the depletion layer is It spreads to area 13. Therefore, the holes that are efficiently absorbed up to the long wavelength end light wavelength corresponding to the bandgap width of the region 13 and generated are collected in the pn junction by the drift electric field. The main characteristics of this prototype pin photodiode are: wavelength sensitivity range of 1.0 to 1.55 μm + quantum efficiency fy5
% (1.3 μm) Junction capacitance o, spF' + dark current is 0.
1 nA (t, oV) or less.

The effects of this embodiment will be explained below.

By using the interface characteristics between the ial InGaAsP layer and the insulating film, the low current can be reduced.

lb) By forming the layer structure as described above, it is possible to prevent an increase in dark current due to the tunnel effect.

(C) By forming the layer structure as described above, photoexcited carriers can be efficiently collected at the junction, resulting in high sensitivity.

+d+ By forming the layer structure as described above, photoexcited carriers can be collected at the junction at a drift speed,
It can be made faster.

(e) By forming the layer structure as described above, the depletion layer cap can be widened, so that the junction capacitance can be reduced, which is effective in increasing the speed of the device.

As another example, there is a case where the incident direction of light is set toward the InP substrate side. FIG. 3 is a sectional view of the device showing this example. The same symbols as in FIG. 2 indicate the same parts. Layer 15 is an InGaAsP layer for surface protection. The difference from the embodiment shown in FIG. 2 is that the electrode 19 removes the metal in the region located below the diffusion region 16, and the electrode 18 is provided over the entire surface since no incident light is required. It is.

Further, although the example of the InP-InGaAsP-based material has been described as an example above, the material system is not limited to this.

For example, an optical semiconductor device having the same purpose can be realized by using a material system mainly composed of Garb, with GaAjSb as the 14th layer, Garb as the 13Ml layer, GaSb as the 12th layer, and GaAjAs8b as the 15ffi layer.

According to the present invention, in addition to stabilizing the interface characteristics of the element,
Since the layer structure takes into consideration the forbidden band width, impurity concentration, and thickness of the device, it is effective in improving the electrical properties (dark current, junction capacitance t) and photoelectric conversion efficiency of the device.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a conventional element structure, and (al
, indicates a mesa structure, and (b) indicates a planar structure. FIGS. 2 and 3 show cross-sectional views of an element structure according to an embodiment of the present invention. Explanation of symbols n 1 ・-=-n+ type InP substrate, 02 ・----
-n-type InGaAsn 3-...p-type 1 n()aA
s, 08 e O9-・” electrode, 1 + 11 =
・=・n+ type InP substrate, 2 ・---n+ type InP
Layer, 12... n-type InP layer, 3, 13...
...n-type InGaAsP layer, 4114---n-type 1
nP layer, 6°16...p-type In (3aAsP diffusion layer, 7.17.17'...insulating film, 15...
...n-type InGaAsP layer, 8°18...p
type electrode, 9.19...n type electrode! fJ+ Tomoe 2 Figure q Sho 3 Figure 1 θ Continuation of page 1 0 Inventor Kuraguchi-Hiroshi 1-280 Higashi Koigakubo, Kokubunji City Hitachi, Ltd. Central Research Laboratory 0 Author Yasushi Koga 1-280 Higashi Koigakubo, Kokubunji City Inside Hitachi, Ltd. Central Research Laboratory

Claims (1)

[Claims] a first semiconductor exhibiting a first conductivity type; and a second semiconductor layer having a wider bandgap than the first semiconductor layer and exhibiting the first conductivity type; There is a layer structure in which a third semiconductor layer exhibiting a first conductivity type is provided on top, a fourth insulating film is provided on the third semiconductor layer, and one of the second and third semiconductor layers is provided. It has a p'n junction in which a fifth region exhibiting the second conductivity type is selectively provided in the second region, and the impurity concentration of the second region is equal to or higher than that of the first region, And the impurity concentration of the first region is 2×1
An optical semiconductor device characterized in that the thickness is 0.016 cm or less.